1. Field of the invention
The present invention relates to a thermal head for use in thermal recording in a facsimile machine, a printer, or the like.
2. Description of the Related Art
In a conventional thermal head, as shown in FIG. 5, an individual electrode 3 connected to one end of a heater resistor 2 is connected to a driving element 5. The other end of the heater resistor 2 is connected to a common electrode 4. All of these components are provided on the same plane on an insulating substrate 1.
The individual electrode 3 and the driving element 5 are connected by wire bonding or flip chip. The driving element 5 and the connecting portion are, for protection, encapsulated with an encapsulation on the periphery of the driving element using an epoxy resin or the like. The encapsulation covers the whole of the driving element 5 and the connecting portion, and further, for the purpose of securing a reliability, has a width and the height which are larger than those of the driving element 5 and the connecting portion. Thus, in order to avoid interference with a platen for advancing paper by rotating together with the paper, the position of the encapsulation is required to be apart from the heater resistor 2 by a predetermined distance. However, on the other hand, in order to lower the cost of the thermal head, it is necessary to make the width of the substrate as small as possible to increase the number of the thermal heads taken from one process unit substrate. Therefore, for example, is made the platen diameter as small as possible to avoid the interference, to realize both decrease in the width of the substrate and to avoid interference between the encapsulation, the paper 9 and the platen 8. However, making the platen diameter small has problems such as insufficient strength and deflection of the platen and a decrease in the amount of collapse (contact area with the paper) by pressing pressure, and thus, is adversely affected the printing quality. Therefore, about 5 mm to 10 mm is thought to be the lower limit of the platen diameter, which means that, in order to avoid the interference with the encapsulation, it is not possible to make the width of the substrate smaller beyond a certain extent.
Since, by the foregoing construction paper is inserted so as to keep out of the encapsulated portion, the paper insert path is curved, and thus, hard cardboard, plastic paper which is difficult to fold, and the like can not be used for printing. Therefore, conventionally, with regard to these kinds of paper which are difficult to fold, in order to secure a straight path (a straight paper insert path), an end face type thermal head as shown in FIG. 6 is provided where the heater resistor 2 is provided on an end face of the substrate and the driving element 5 is provided perpendicularly to the heater resistor 2 and a near edge type thermal head as shown in FIG. 7 where the interference with the encapsulated portion is avoided by providing the heater resistor 2 at an edge portion of the substrate and slanting the thermal head. Further, recently, a method has been thought of where, as shown in FIG. 8, a concave portion is processed in a part of the insulating substrate 1 such that a step is provided in the substrate itself for making a portion where the driving element 5 is provided lower than the heater resistor 2.
However, with regard to all of the above-described methods, since the shape of the substrate is complicated, its processing is difficult, and, since its patterning has to be carried out with regard to different surfaces or a surface having a great step, the manufacturing method is complicated and it is difficult to lower the cost.